What Chemical to Use to Decrease Pool pH

By J. Lang Wood

Keeping your swimming water in sanitary condition requires a careful balance of pool chemicals. The water’s pH, or the measure of acidity or alkalinity of the water, is a crucial element of this chemistry. Without the proper pH level, pool chemicals cannot work effectively. Generally, your pool manufacturer provides recommendations on what chemicals to use to decrease or increase the pH of the water in your pool.

Pool Water Testing

Swimming pool maintenance requires the use of water testing kits that indicate the pH range, chlorine levels and calcium hardness. Pool kits come in a variety of forms, the simplest being “strips” that you dip in the water that change color to indicate the levels of chemicals available. Do testing for pH weekly and adjust as needed.

Problems of High pH

When the pH of pool water is too high, you may see calcium buildup on the surfaces or at the waterline. Pool water may become cloudy or dull. The filter elements can clog. You may experience burning nose and eyes or dry itchy skin. Algae may build up due to ineffective sanitizing of chlorine.

Decreasing Pool pH

Making the water more acidic lowers the pH value of the pool water. Do this by adding muriatic acid, sold at pool supply and home improvement stores, to the pool water. Muriatic acid, also called hydrochloric acid, generally comes in a 30 to 35 percent solution. Sodium bisulfate is also commonly used. Nitric acid is also available but is highly corrosive to pool parts. Sulfuric acid also lowers pool water pH. Adjust incrementally and test until the pH is in the recommended range of 7.4 to 7.6, according to POOLplaza.

Amount to Use

Decreasing the pH level of the pool requires fine tuning of the chemicals in the water. Add a small amount of muriatic acid at a time and then re-test to see how close you are to the recommended range. Add more, if necessary. For instance, if the pool pH is at 7.8 and you want to get it down to 7.6, add 1 1/3 cups of muriatic acid for a 10,000-gallon pool, according to BackyardCityPools. Dilute the acid with water before adding to the pool water. A 15,000-gallon pool needs 2 cups of muriatic acid, and a 20,000-gallon pool would require 2 1/2 cups of muriatic acid, to get the pH down to 7.6.

Pool Chemical Safety

Pool chemicals give off toxic fumes that can be hazardous. Use only in open, well-ventilated areas, and use according to label directions. Protect skin and eyes from chemical burns. Clothing can be bleached or damaged by pool chemicals.